title: Proton pump inhibition induces autophagy as a survival mechanism following oxidative stress in human melanoma cells.
abstract: Proton pump inhibitors (PPI) target tumour acidic pH and have an antineoplastic effect in melanoma. The PPI esomeprazole (ESOM) kills melanoma cells through a caspase-dependent pathway involving cytosolic acidification and alkalinization of tumour pH. In this paper, we further investigated the mechanisms of ESOM-induced cell death in melanoma. ESOM rapidly induced accumulation of reactive oxygen species (ROS) through mitochondrial dysfunctions and involvement of NADPH oxidase. The ROS scavenger N-acetyl-L-cysteine (NAC) and inhibition of NADPH oxidase significantly reduced ESOM-induced cell death, consistent with inhibition of cytosolic acidification. Autophagy, a cellular catabolic pathway leading to lysosomal degradation and recycling of proteins and organelles, represents a defence mechanism in cancer cells under metabolic stress. ESOM induced the early accumulation of autophagosomes, at the same time reducing the autophagic flux, as observed by WB analysis of LC3-II accumulation and by fluorescence microscopy. Moreover, ESOM treatment decreased mammalian target of rapamycin signalling, as reduced phosphorylation of p70-S6K and 4-EBP1 was observed. Inhibition of autophagy by knockdown of Atg5 and Beclin-1 expression significantly increased ESOM cytotoxicity, suggesting a protective role for autophagy in ESOM-treated cells. The data presented suggest that autophagy represents an adaptive survival mechanism to overcome drug-induced cellular stress and cytotoxicity, including alteration of pH homeostasis mediated by proton pump inhibition.
authors.affiliation: Department of Therapeutic Research and Medicines Evaluation, Unit of Antitumor Drugs, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: M L
authors.initials: ML
authors.lastname: Marino
authors.forename: S
authors.initials: S
authors.lastname: Fais
authors.forename: M
authors.initials: M
authors.lastname: Djavaheri-Mergny
authors.forename: A
authors.initials: A
authors.lastname: Villa
authors.forename: S
authors.initials: S
authors.lastname: Meschini
authors.forename: F
authors.initials: F
authors.lastname: Lozupone
authors.forename: G
authors.initials: G
authors.lastname: Venturi
authors.forename: P
authors.initials: P
authors.lastname: Della Mina
authors.forename: S
authors.initials: S
authors.lastname: Pattingre
authors.forename: L
authors.initials: L
authors.lastname: Rivoltini
authors.forename: P
authors.initials: P
authors.lastname: Codogno
authors.forename: A
authors.initials: A
authors.lastname: De Milito
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D064098:Esomeprazole / Q000627:therapeutic use*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008545:Melanoma / Q000188:drug therapy* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D019255:NADPH Oxidases / Q000378:metabolism; D018384:Oxidative Stress; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D054328:Proton Pump Inhibitors / Q000627:therapeutic use*; D017382:Reactive Oxygen Species / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D010750:Phosphoproteins; D054328:Proton Pump Inhibitors; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D064098:Esomeprazole; D000111:Acetylcysteine